A system and method of the above type is known from US patent application US 2006/0110008.
In this document a number of markers are provided and at least one marker of which the corneal reflection is within a threshold distance of the pupil centre is identified or at least two markers having a corneal reflection close to the centre of the pupil. The identified marker or markers are indicative of the observer's point of gaze at the object.
Continuous measurement of the viewing direction or also called gaze is commonly referred to as ‘gaze-tracking’ (often the more ambiguous term ‘eye-tracking’ is used). There are various methods to perform gaze tracking Video capture has shown to be a viable option for remote and truly unobtrusive gaze tracking. However, virtually all gaze tracking systems require a user-specific calibration after which the user is allowed only little head movement. Consequently, these systems are confined to desktop usage and not suitable for consumer applications. In consumer applications, user-specific calibration is not a realistic option. Calibration-free gaze tracking is widely pursued by several research centres, often by extrapolating on the basis of existing concepts (more cameras, more processing). The observer can be a human, whether an adult or a child, but also an animal.
US 2006/0110008 attempts to remedy the problem and to provide a calibration-free system and method. In the situation that the eye is gazing at a light source, its reflection in the cornea appears to coincide with the pupil centre. The system and method of 2006/011008 provides a number of markers on the object. In the recorded image of eye the marker having a corneal reflection within a threshold distance of the pupil centre, or a number of markers having a corneal reflection close to the pupil centre are identified. These are used to estimate the direction of gaze.
However, the known system has a number of shortcomings:                each of the markers has to be labelled. This condition requires a number of video frames to be analysed before identification of a marker can be made. This introduces latency in the gaze tracking. Given the motility of the eye, temporal latency quickly gives rise to motion artefacts.        Where one marker is used, there is always an inaccuracy equivalent to the threshold distance in the accuracy of the established gaze direction.        Where more than one marker is used interpolation is required. This requires computation power and introduces inaccuracies.        